using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading.Tasks;

namespace Elwig.Helpers.Export {
    public abstract class Csv<T> : IExporter<T> {
        public static string FileExtension => "csv";

        protected readonly StreamWriter Writer;
        protected readonly char Separator;
        protected string? Header;

        public Csv(string filename, char separator = ';') : this(filename, separator, Encoding.UTF8) { }

        public Csv(string filename, char separator, Encoding encoding) {
            Writer = new StreamWriter(filename, false, encoding);
            Separator = separator;
        }

        public void Dispose() {
            GC.SuppressFinalize(this);
            Writer.Dispose();
        }

        public ValueTask DisposeAsync() {
            GC.SuppressFinalize(this);
            return Writer.DisposeAsync();
        }

        public async Task ExportAsync(IEnumerable<T> data) {
            if (Header != null) await Writer.WriteLineAsync(Header);
            foreach (var row in data) {
                await Writer.WriteLineAsync(FormatRow(row));
            }
        }

        public void Export(IEnumerable<T> data) {
            ExportAsync(data).GetAwaiter().GetResult();
        }

        public string FormatRow(IEnumerable row) {
            return string.Join(Separator, row);
        }

        public abstract string FormatRow(T row);
    }
}